Why would you want to have data unless you need it? I have 250 odd contacts and assuming each dp (display picture; avatar as you called it) is about 50kb, that would make 12.21 MB every time a refresh was made. I am on a 64kbps connection so that would take me 26 odd minutes
Assuming a broadband connection (256 kbps; standard), it would be 48 seconds. You'd need a really 20MBit connection for 250 contacts (with dps of 50 kb each) to download all dps in 5 seconds (which would be the maximum acceptable time in my opinion).
What I'm trying to say is that its not useful to download dps all at once and keep doing this again and again. Its rather simpler to do this on a need to know basis like when you click for someone's personal info or when ever the dp needs to actually be shown on screen
Hope this explanation helps
/ 
